thick ‧ en /ˈθɪkən/ BrE AmE verb [intransitive and transitive]
[ Word Family: noun : ↑ thick , ↑ thickness , ↑ thickener , thickening, ↑ thicko ; verb : ↑ thicken ; adverb : ↑ thickly ; adjective : ↑ thick ]
to become thick, or make something thick OPP thin :
The fog was beginning to thicken.
Thicken the soup by adding potatoes.
thicken something with something
a stew thickened with lentils and vegetables
⇨ the plot thickens at ↑ plot 1 (3)